Living electrodes with bacteria and organic electronics
by Monica Westman Svenselius / 26 November 2018
“Adding bacteria to electrochemical systems is often an environmentally sensitive means to convert chemical energy to electricity. Applications include water purification, bioelectronics, biosensors, and for the harvesting and storage of energy in fuel cells. One problem that miniaturisation of the processes has encountered is that a high signal strength requires large electrodes and a large volume of liquid. Researchers at Linköping University, together with colleagues at the Lawrence Berkeley National Laboratory in Berkeley, California, USA, have now developed a method in which they embed the electroactive bacterium Shewanella oneidensis into PEDOT:PSS, an electrically conducting polymer, on a substrate of carbon felt.
The researchers call the result a “multilayer conductive bacterial-composite film”, abbreviated as MCBF. Microscopic analysis of the film shows an interleaved structure of bacteria and conducting polymers that can be up to 80 µm thick, much thicker than it can be without this specific technique. “Our experiments show that more than 90% of the bacteria are viable, and that the MCBF increases the flow of electrons in the external circuit.
When our film is used as anode in microbial electrochemical cells, the current is 20 times higher than it is when using unmodified anodes, and remains so for at least several days”, says Gábor Méhes, researcher at Linköping University and one of the lead authors of the scientific article recently published in Scientific Reports. Previous work has tested, among other things, carbon nanotubes to increase the surface area at the anode, but the results were poor.
The possibility to couple biological processes with readable electrical signals is also valuable, for example for environmental sensors which require rapid response times, low energy consumption, and the ability to use many different receptors. Researchers have recently demonstrated how to use Shewanella oneidensis to produce electrical currents in response to arsenic, arabinose (a type of sugar) and organic acids, among others. “
This technology represents a type of “living electrode” where the electrode material and the bacteria are amalgamated into a single electronic biofilm. As we discover more about the essential role that bacteria play in our own health and wellness, such living electrodes will likely become versatile and adaptable tools for developing new forms of bioelectronic technologies and therapies”, says Daniel Simon, principal investigator in Organic Bioelectronics at the Laboratory of Organic Electronics.”
Wired Bacteria Form Nature’s Power Grid
by Carl Zimmer / July 1, 2019
“At three o’clock in the afternoon on September 4, 1882, the electrical age began. The Edison Illuminating Company switched on its Pearl Street power plant, and a network of copper wires came alive, delivering current to a few dozen buildings in the surrounding neighborhood. One of those buildings housed this newspaper. As night fell, reporters at The New York Times gloried in the steady illumination thrown off by Thomas Edison’s electric lamps.
“The light was soft, mellow, and grateful to the eye, and it seemed almost like writing by daylight,” they reported in an article the following day. But nature invented the electrical grid first, it turns out. Even in 1882, thousands of miles of wires were already installed in the ground in the New York region — in meadows, in salt marshes, in muddy river bottoms. They were built by microbes, which used them to shuttle electricity.
“Illustration of the four models for direct electron transfer by a gram-positive bacterium. Biofilm contained redox mediator (a), “nanowires” (b), conductive cell walls (c), or cytochrome chain linking the inner membrane to cell surface (d). Ferric iron is shown as a representative exogenous electron acceptor.”
Electroactive bacteria were unknown to science until a couple of decades ago. But now that scientists know what to look for, they’re finding this natural electricity across much of the world, even on the ocean floor. It alters entire ecosystems, and may help control the chemistry of the Earth. “Not to sound too crazy, but we have an electric planet,” said John Stolz, a microbiologist at Duquesne University in Pittsburgh.
In the mid-1980s, Dr. Stolz was helping to study a baffling microbe fished out of the Potomac River by his colleague Derek Lovley. The microbe, Geobacter metallireducens, had a bizarre metabolism. “It took me six months to figure out how to grow it in the lab,” said Dr. Lovley, now a microbiologist at the University of Massachusetts at Amherst.
Like us, Geobacter feed on carbon compounds. As our cells break down these compounds to generate energy, they strip off free electrons and transfer them to oxygen atoms, producing water molecules. Geobacter couldn’t use oxygen, however, because it lived at the bottom of the Potomac, where the element was in short supply. Instead, Geobacter transfers its electrons to iron oxide, or rust, Dr. Lovley and his colleagues discovered.
The process helps turn rust into another iron compound, called magnetite. The finding left the scientists with a puzzle. We humans draw oxygen into our cells to utilize it, but Geobacter does not import rust. So the microbe must somehow get the electrons out of its cell body and attach them to rust particles. How?
The researchers struggled for years to find the answer. Dr. Stolz eventually turned to other microbes to study. But Dr. Lovely soldiered on. Over the years, he and his colleagues have come across Geobacter in many places far beyond the Potomac. They’ve even encountered the bacteria in oil drilled from deep underground. “It’s basically found everywhere,” Dr. Lovley said.
In the early 2000s, Dr. Lovely’s team discovered that Geobacter could sense rust in its neighborhood. The microbe responded by sprouting hairlike growths. Maybe each of those growths, known as a pilus, was actually a wire that latched onto the rust, Dr. Lovley thought. Electrons could flow from the bacterium down the wire to the receptive rust. “It seemed like a wild idea at the time,” Dr. Lovley said. But he and his team found several clues suggesting that the pilus is indeed a living wire.
In one experiment, when Geobacter was prevented from making pili, the bacteria couldn’t turn rust to magnetite. In another, Dr. Lovely and his colleagues plucked pili from the bacteria and touched them with an electrified probe. The current swiftly shot down the length of the hairs. Subsequent research revealed that Geobacter can deploy its wires in different ways to make a living.
Not only can it plug directly into rust, it can also plug into other species of microbes. The partners of Geobacter welcome the incoming flow of electrons. They use the current to power their own chemical reactions, which convert carbon dioxide into methane.
Discoveries like these raised the possibility that other bacteria might be dabbling in electricity. And in recent years, microbiologists have discovered a number of species that do. “When people are able to dig down at the molecular level, we’re finding major differences in strategy,” said Jeff Gralnick of the University of Minnesota. “Microbes have solved this issue in several different ways.
In the early 2000s, a Danish microbiologist named Lars Peter Nielsen discovered a very different way to build a microbial wire. He dug up some mud from the Bay of Aarhus and brought it to his lab. Putting probes in the mud, he observed the chemical reactions carried out by its microbes. “It developed in a very weird direction,” Dr. Nielsen recalled. At the base of the mud, Dr. Nielsen observed a buildup of a foul-smelling gas called hydrogen sulfide.
That alone was not surprising — microbes in oxygen-free depths can produce huge amounts of hydrogen sulfide. Normally, the gas rises the surface, where oxygen-breathing bacteria can break most of it down. But the hydrogen sulfide in the Aarhus mud never made it to the surface. About an inch below the top of the mud, it disappeared; something was destroying it along the way.
After weeks of perplexity, Dr. Nielsen woke up one night with an idea. If the bacteria at the bottom of the mud broke hydrogen sulfide without oxygen, they would build up extra electrons. This reaction could only take place if they could get rid of the electrons. Maybe they were delivering them to bacteria at the surface. “I imagined it could be electric wires, and I could explain all of this,” he said. So Dr. Nielsen and his colleagues looked for wires, and they found them.
But the wires in the Aarhus mud were unlike anything previously discovered. Each wire runs vertically up through the mud, measuring up to two inches in length. And each one is made up of thousands of cells stacked on top of each other like a tower of coins. The cells build a protein sleeve around themselves that conducts electricity.
As the bacteria at the bottom break down hydrogen sulfide, they release electrons, which flow upward along the “cable bacteria” to the surface. There, other bacteria — the same kind as on the bottom, but employing a different metabolic reaction — use the electrons to combine oxygen and hydrogen and make water.
Cable bacteria are not unique to Aarhus, it turns out. Dr. Nielsen and other researchers have found them — at least six species so far — in many places around the world, including tidal pools, mud flats, fjords, salt marshes, mangroves and sea grass beds. And cable bacteria grow to astonishing densities. One square inch of sediment may contain as much as eight miles of cables. Dr. Nielsen eventually learned to spot cable bacteria with the naked eye. Their wires look like spider silk reflecting the sun.
“The stratified layers of the Earth’s atmosphere: troposphere, stratosphere, and upper atmosphere. The stratosphere is located approximately 30-50km above the Earth’s surface. This region is where B. stratosphericus can be found (1,5).”
Electroactive microbes are so abundant, in fact, that researchers now suspect that they have a profound impact on the planet. The bioelectric currents may convert minerals from one form to another, for instance, fostering the growth of a diversity of other species. Some researchers have speculated that electroactive microbes may help regulate the chemistry of both the oceans and the atmosphere. “To me, it’s a strong reminder of how ready we are to ignore things we cannot imagine,” Dr. Nielsen said.
Much about these microbes remains murky, and subject to debate. In April, Nikhil S. Malvankar, a physicist at Yale University, and his colleagues challenged Dr. Lovely’s finding that Geobacter use pili as wires. Their research indicates that bacteria use a different structure to pump electrons. It’s a wire built from building blocks called cytochromes. Individual cytochromes are important for moving electrons around inside cells.
But until now no one knew they could be stacked into a conductive wire.N“There never had been a material like this before,” Dr. Malvankar said. Sarah Glaven, a research biologist at the United States Naval Research Laboratory who was not involved in the new study, said she found it compelling. “Totally believe it,” she said. “The question is, is it just part of the puzzle?” It’s possible that Geobacter uses both structures to move electrons, Dr. Glaven said.
Or maybe one serves a different function, and just happens to conduct electricity in the hands of a scientist. The answers to such questions matter deeply to scientists, who are tinkering with electroactive bacteria to develop new kinds of technology. At Cornell University, Buz Barstow and his colleagues are investigating the possibility of wiring bacteria to solar panels. The panels would capture sunlight and generate a stream of electrons. The electrons would stream down microbial wires to a species of bacteria called Shewanella, which would use the energy to convert sugar into fuel.
“(A) A generalized model of the S. oneidensis electron outflow machinery: A, MtrA; B, MtrB; C, MtrC; D, OmcA; I, the complex I NADH quinone oxidoreductase; and Q, CymA. (B) A generalized model of the proposed electron uptake machinery used by the neutrophilic iron-oxidizing microbe Sideroxydans lithotrophicus. ? denotes parts of the electron uptake machinery responsible for reduction of NAD(P)+ that are still unknown.”
It’s still a distant dream. For now, Dr. Barstow is trying to work out the basic biology by which Shewanella moves electrons from its wires to the molecules it uses for its metabolism. But he is so taken with the elegance of electroactive bacteria that he figures it’s worth a shot. “You’re talking to someone who has drunk the Kool-Aid,” he said. Other researchers are looking into using these filaments as sensors.
“Scientists sponsored by the Office of Naval Research have genetically engineered a strain of bacteria found naturally in dirt to create electrical wires thousands of times thinner than a human hair.”
For instance, a wristband with embedded wires might monitor people’s health by delivering electric current when it detects chemical changes in sweat. Dr. Lovley and his colleagues are genetically engineering Geobacter to add molecular hooks to their pili, so that they snag certain molecules.
Among the many advantages that living wires may have is that they’d be easier on the environment than the man-made kind. “It takes a lot of energy and nasty chemicals to make a lot of those electronic materials, and then none of them are biodegradable,” Dr. Lovley said. Bacteria, by contrast, can build wires from little more than sugar. And when it comes time to throw wires away, they become food for other microbes.
“Scientist Moh El-Naggar studies bacteria that construct membrane wires to “breathe” rock. This three-dimensional construct depicts a wire composed of spherical vesicles containing electron-transporting proteins (red and green).”
Dr. Nielsen, who now directs the Center for Electromicrobiology at the University of Aarhus in Denmark, said that he is avoiding the technology rush for now. There is still too much to learn about the microbes themselves. “Once we find out what these wires are made from and how they work, a lot of potential applications may show up,” he said.”
BREATHING METAL – MINERAL RESPIRATION
Gut bacteria produce electricity
by Robert Sanders / September 12, 2018
“While bacteria that produce electricity have been found in exotic environments like mines and the bottoms of lakes, scientists have missed a source closer to home: the human gut. UC Berkeley scientists discovered that a common diarrhea-causing bacterium, Listeria monocytogenes, produces electricity using an entirely different technique from known electrogenic bacteria, and that hundreds of other bacterial species use this same process.
Many of these sparking bacteria are part of the human gut microbiome, and many, like the bug that causes the food-borne illness listeriosis, which can also cause miscarriages, are pathogenic. The bacteria that cause gangrene (Clostridium perfringens) and hospital-acquired infections (Enterococcus faecalis) and some disease-causing streptococcus bacteria also produce electricity. Other electrogenic bacteria, like Lactobacilli, are important in fermenting yogurt, and many are probiotics.
“The fact that so many bugs that interact with humans, either as pathogens or in probiotics or in our microbiota or involved in fermentation of human products, are electrogenic — that had been missed before,” said Dan Portnoy, a UC Berkeley professor of molecular and cell biology and of plant and microbial biology. “It could tell us a lot about how these bacteria infect us or help us have a healthy gut.” The discovery will be good news for those currently trying to create living batteries from microbes. Such “green” bioenergetic technologies could, for example, generate electricity from bacteria in waste treatment plants. The research will be posted online Sept. 12 in advance of Oct. 4 print publication in the journal Nature.
“Bacterial electron-transfer pathways.”
Bacteria generate electricity for the same reason we breathe oxygen: to remove electrons produced during metabolism and support energy production. Whereas animals and plants transfer their electrons to oxygen inside the mitochondria of every cell, bacteria in environments with no oxygen — including our gut, but also alcohol and cheese fermentation vats and acidic mines — have to find another electron acceptor. In geologic environments, that has often been a mineral — iron or manganese, for example — outside the cell. In some sense, these bacteria “breathe” iron or manganese.
“G. metallireducens, known for “breathing” iron oxides“
Transferring electrons out of the cell to a mineral requires a cascade of special chemical reactions, the so-called extracellular electron transfer chain, which carries the electrons as a tiny electrical current. Some scientists have tapped that chain to make a battery: stick an electrode in a flask of these bacteria and you can generate electricity.
The newly discovered extracellular electron transfer system is actually simpler than the already known transfer chain, and seems to be used by bacteria only when necessary, perhaps when oxygen levels are low. So far, this simpler electron transfer chain has been found in bacteria with a single cell wall — microbes classified as gram-positive bacteria — that live in an environment with lots of flavin, which are derivatives of vitamin B2. “It seems that the cell structure of these bacteria and the vitamin-rich ecological niche that they occupy makes it significantly easier and more cost effective to transfer electrons out of the cell,” said first author Sam Light, a postdoctoral fellow. “Thus, we think that the conventionally studied mineral-respiring bacteria are using extracellular electron transfer because it is crucial for survival, whereas these newly identified bacteria are using it because it is ‘easy.’”
To see how robust this system is, Light teamed up with Caroline Ajo-Franklin from Lawrence Berkeley National Laboratory, who explores the interactions between living microbes and inorganic materials for possible applications in carbon capture and sequestration and bio-solar energy generation. She used an electrode to measure the electric current that streams from the bacteria — up to 500 microamps — confirming that it is indeed electrogenic. In fact, they make about as much electricity — some 100,000 electrons per second per cell — as known electrogenic bacteria. Light is particularly intrigued by the presence of this system in Lactobacillus, bacteria crucial to the production of cheese, yogurt and sauerkraut. Perhaps, he suggests, electron transport plays a role in the taste of cheese and sauerkraut. “This is a whole big part of the physiology of bacteria that people didn’t realize existed, and that could be potentially manipulated,” he said.
Light and Portnoy have many more questions about how and why these bacteria developed such a unique system. Simplicity — it’s easier to transfer electrons through one cell wall rather than through two — and opportunity — taking advantage of ubiquitous flavin molecules to get rid of electrons – appear to have enabled these bacteria to find a way to survive in both oxygen-rich and oxygen-poor environments. Other co-authors are Lin Su and Jose A. Cornejo of Berkeley Lab and Rafael Rivera-Lugo, Alexander Louie and Anthony T. Iavarone of UC Berkeley. The research was funded by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health and the Office of Naval Research.”
ASTROBIOLOGY – RADIATION RESISTANT FUNGI (cont.)
Space station mold survives 200 times the radiation dose that would kill a human
by Richard A. Lovett / Jun. 28, 2019
“As anyone who’s ever had a mold infestation knows, the fungi can be very hard to kill. It turns out mold may also be highly resistant to the harsh conditions of outer space. Its spores can survive doses of radiation 200 times higher than those that would kill a human, researchers reported here today at the Astrobiology Science Conference. Such hardiness could make it difficult to eliminate mold’s health risks to astronauts. Mold might also one day threaten other parts of the solar system—with hitchhiking mold spores from Earth. Astronauts on the International Space Station (ISS) already constantly battle with mold, which grows on the station’s walls and equipment. That mold, of course, is in a protected structure in low-Earth orbit, where radiation doses are low. Outside of the station, doses are higher—and they would be higher still on the hull of a spacecraft going to Mars or beyond.
To find out what might happen to mold there, Marta Cortesão, a microbiologist at the German Aerospace Center (DLR) in Cologne and colleagues beamed x-rays and heavy ions at a common black mold called Aspergillus niger, which is plentiful in the ISS. The researchers fired “stupid amounts” of radiation, Cortesão says—much more than encountered on a Mars-bound spaceship (0.6 gray per year) or on the surface of Mars (0.2 gray per year). The gray is a measure of the amount of absorbed radiation energy.
The researchers discovered that the spores could survive radiation doses of 500 to 1000 gray, depending on which type of radiation they were exposed to. Humans, by contrast, get radiation sickness at doses of 0.5 gray and are killed by 5 gray. Cortesão also found that the spores survived large amounts of high-energy ultraviolet radiation, which is commonly used as a hospital disinfectant and has been proposed for sterilizing the surfaces of spacecraft.
Cortesão cautions that her research focused only on radiation and did not include all aspects of the harsh outer space environment. But, she says, at least one older study suggests that mold spores resist radiation even better in a vacuum. Meanwhile, one thing is certain, she says: “We will have spores with us for sure in our space travels. Fungi have been forgotten for the past 20 or 30 years, but it’s time to go back to them.” Andrew Schuerger, a microbiologist and Mars astrobiologist at the University of Florida in North Merritt Island, agrees. Most of the focus on keeping Earth’s microorganisms from contaminating other worlds so far has been on bacteria, he says, because the vast bulk of microorganisms on the surfaces of spacecraft has been bacterial. “I really like a presentation like this [that says] ‘Let’s not forget about this other group of microorganisms called fungi,’” he says.
“Cladosporium sphaerospermum discovered at the Chernobyl site. There were as many as 200 species of fungi isolated growing around the site. Some of which were not only thriving in the presence of radiation, but actually growing towards the source.”
The finding is also important for researchers studying the origin of life, says Paul Mason, an astrobiologist at New Mexico State University in Las Cruces. That’s because one of the puzzles in origin-of-life research is that Earth seems to have gone from prebiotic all the way to fairly complex microorganisms early in its history—a process that some scientists think required more time than had passed since the planet first became habitable. One idea, Mason says, is that life originated elsewhere, either in our solar system or farther afield. “Now that we know that Earth life can survive in space, it is certainly reasonable to think that it could have arrived on Earth from somewhere else,” he says.”
BACTERIAL POWER CORDS FOUND in SEABED
FLYING ELECTRIC SPIDERS